Two shots of my Honeywell Pentax H3 I picked up two years ago on Ebay as an impulse purchase. It suffered from a stalled mirror which is common with old Pentax screwmount cameras and that is due to the shutter curtains not going through it's complete cycle.
In my current between opportunities state, a professional CLA (clean lubricate and align) is a little expensive so I went to Pentax-Manuals.com downloaded the repair manual for the Asahi Pentax S3 which is the same camera as the H3. I then also downloaded another how to link on the Instructables site on how to fix a seized mirror on a Pentax Spotmatic ES.
Bear in mind the Spotmatic ES was made at least ten years later than the H3/S3 and the insides would have evolved a little bit. However combined with the S3 service manual, I have some direction.
Old Pentaxes are reasonably easy to fix, if you have steady hands and high spatial reasoning. If you have an old body you got for stupid cheap, you will get a tutorial on how a mechanical camera works.